Dynamic Adaptation of Contention Window Sizes in IEEE 802. lie Wireless LAN

The IEEE 802.11e is currently standardizing a MAC protocol, which provides EDCA (enhanced distributed channel access) and HCCA (HCF controlled channel access) to support differentiation service over WLAN (wireless LAN). The differentiation service provided by EDCA is achieved based on different CW (contention window) sizes. Under EDCA, realtime traffic can have a better opportunity to access the WM (wireless medium). However, even if a real-time flow can win competitions with a non real-time (e.g. best effort) flow in a STA (station), it has to compete with other flows transmitted from other STAs. Since default CW sizes for real-time flows are set to small values in order to achieve the service differentiation, real-time flows cannot meet their requirements when collisions between real-time flows often occur. Therefore, this paper focuses on trying to reduce collisions to protect real-time traffic from performance degradation. Since large values set to default CW sizes generates large channel access delay even when there are little real-time flows associating with an AP, we propose an algorithm to adaptively change CW sizes. Simulation results show that our proposed algorithm overcome throughput degradation under EDCA